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Nuclear Fuels and Fission

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Nuclear fission occurs when a stable isotope is struck by a neutron. The isotope absorbs the neutron, becomes unstable and then splits apart, releasing large amounts of energy.

What is nuclear fission?

The fission of 1 kilogram of uranium-235 releases more energy than burning 2 million kilograms of coal!

Unlike natural radioactive decay, fission is not a natural event.

Isotopes that undergo fission include uranium-235 and plutonium-239. Most nuclear reactors use uranium-235.

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There are two major isotopes of uranium – 238 and 235. Uranium-238 is more common, but it does not undergo nuclear fission.

Only 0.7% of naturally-occurring uranium is uranium-235, which does undergo nuclear fission.

The enriched fuel is made into rods which are used in the reactor.

Before it can be used as the fuel in nuclear power stations, uranium needs to be enriched until it has 3% uranium-235.

How is uranium used in nuclear reactors?

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What happens in nuclear fission?

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What are the products of fission?

When fission of uranium-235 occurs, it splits into two smaller nuclei, known as daughter nuclei.

Many possible daughter nuclei may be formed in a fission process. One example is shown below.

+ +

neutronuranium235

strontium90

xenon144

fission

+

neutrons+ + + uranium236

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In this decay equation, the number of protons and the mass numbers on both sides of the equation balance.

Where does the energy come from?

Barium and krypton are often the daughter nuclei formed by the fission of uranium-235. The decay equation for this is:

The mass that has been lost has turned into energy.

235 1 90 143 192 0 36 56 0

U + n Kr Ba+ n3 +

However, the particles after decay have slightly less mass than the particles before decay.

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How does nuclear power work?

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Nuclear fission – true or false?

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